Novel process for the production of methylol

ABSTRACT

The reaction of isobutylene and methylal to form a mixture 1,3dimethoxy-3-methyl butane and 4-methoxy-2-methylbutene-1 and rearrangement of the same to yield isoprene and methanol is disclosed herein. The isobutylene and methylal may be obtained by the oxidation of isobutane to form t-butylhydroperoxide, followed by rearrangement of the hydroperoxide to yield methylal and tbutyl alcohol and dehydration of the alcohol to produce isobutylene.

United States Patent 1191 Turner NOVEL PROCESS FOR THE PRODUCTION OF METHYLOL [75] Inventor: John O. Turner, West Chester, Pa.

[73] Assignee: Sun Research and Development Co., Marcus Hook, Pa.

22] Filed: Apr. 27, 1973 211 Appl. No.: 355,123

Related U.S. Application Data [62] Division of Ser. No. 126,934, March 22, 1971. Pat.

[52] U.S. Cl. 260/615 A; 260/632 R; 260/632 C [51] Int. Cl. C07c 43/30 [58] Field of Search 260/615 A, 632 R, 632 C [56] References Cited UNITED STATES PATENTS 2,663,742 12/1953 Freval et a1 260/615 A 3,737,518 6/1973 Bonetti et al. 260/632 R 3,758,598 9/1973 Turner 260/615 A OTHER PUBLICATIONS Hawkins et al., J. Chem. Soc. (1950), pp. 2804-2805.

Primary Examiner-Howard T. Mars A Attorney, Agent, or Firm-George L. Church; Donald R. Johnson; Stanford M. Back [57] ABSTRACT The reaction of isobutylene and methylal to form a mixture 1,3-dimethoxy-3-methyl butane and 4-methoxy-2-methylbutene-l and rearrangement of the same to yield isoprene and methanol is disclosed herein. The isobutylene and methylal may be obtained by the oxidation of isobutane to form tbutylhydroperoxide, followed by rearrangement of the hydroperoxide to yield methylal and t-butyl alcohol and dehydration of the alcohol to produce isobutylene.

3 Claims, No Drawings NOVEL PROCESS FOR THE PRODUCTION OF METHYLOL This is a division of application Ser. No. 126,934 filed Mar. 22, 1971, now U.S. Pat. No. 3,758,610.

CROSS-REFERENCE TO RELATED CASES Step 2 of the process described below is related to earlier-filed application, Ser. No. 98,036 filed Dec. 14, I970, now U.S. Pat. No. 3,758,598, in the name of John O. Turner, and which is a continuation-in-part of Ser. No. 873,093 filed Oct. 31, 1969, and now abancloned, by the same inventor, and entitled IM- PROVED SYNTHESIS OF ALIPHATIC AND ALI- CYCLIC ETHERS."

BACKGROUND OF THE INVENTION This invention relates to a novel method for the preparation of isoprene. More particularly, this invention relates to a process whereby isobutylene and methylal are reacted to form a mixture of 1,3-climethoxy-3- methylbutane and 4-methoxy-2-methylbutene-l containing small amounts of isoprene and methyl t-butyl ether, which, when heated with acid rearranges to form isoprene and methanol. The isobutylene and methylal are both desirably derived from a series of steps comprising the oxidation of isobutane to form a mixture of t-butyl-hydroperoxide and t-butyl alcohol, followed by the reaction of the t-butyl-hydroperoxide with methanol under acid conditions to form methyl-a] and additional t-butyl alcohol. The t-butyl alcohol may then be dehydrated to provide isobutylene.

PRIOR ART Known prior art which appears relevant to each of the steps of the process discussed hereinbelow is as follows:

STEP 1: Discussed in Step I of the Description of the Invention below.

STEP 2: U.S. application, Ser. No. 98,036 filed in December, I970, in the name of John O. Turner and entitled IMPROVED SYNTHESIS OF ALIPHATIC AND ALICYCLIC ETHERS." In that case, however. as distinguished from the instant one, the acid concentration is substantially higher and as a result methyl tbutyl ether is formed rather than butanol.

STEP 3: Discussed in Step 3 of the Description of the Invention below.

STEP 4: JACS 74, 4595 (1952), which teaches the reaction of isobutene with methylal to form chiefly l,3-dimethoxy-3rmethyl butane. This article does not. however, teach or suggest the conversion of the methoxy butanes to isoprene.

STEP 5: U.S. Pat. No. 2,739,995, which teaches treating 2-methyl-2,4-dimethoxy butane at temperatures as low as possible. and preferably at 75 to 165 C in the presence of an acid catalyst, to form isoprene. The formation of other conjugated dienes from compounds such as l,3-dimethoxy-3-methyl butane are likewise suggested by this reference. It has been found. however, that when this latter material is reacted under the temperature conditions taught by the reference, little or no isoprene is formed.

SUMMARY OF THE INVENTION The above reactions may best be illustrated by the following equations:

SUMMARY OF THE INVENTION The above reactions may best be illustrated by the following squat i ons:

2 i-C H 1.5 0 ica l cooa (CH 3 0 Isobutane T-Butyl T-Butyl Hydroperoxidc Alcohol 2 (CH 000a 3 ca 3GB 5 (ocn (CH COH 21-1 0 I Butyl Methanol Methylal T-Butyl Hydroperoxide Alcohol 3. 2 (CH 00a a 2 (01 0 01-1 21 0 T-Butyl lsobutylene Alcohol 0CH3 OCH3 OCH3 CH3 I I I I 3 2 C airflow- 9(Cl-I C-CH -CH cn -cn -c ca;

Isobutylene Methy lal H-Methoxy-Z- l B-Dirne thox'y 3-methy1 Methy Butane Butene-l Table Continued 9 CH2=CH-=CH2 isoprene OCE- C u. k a N P (fDCh CH (3H '-:Cl'i3l2C=-cH2-CE.2 CH2QH-C CH2 CH2 Cl'l-C' CH2? 3., 3-Dimethoxy- 3- t-Methoxy2- Isoprene Methyl Butane Methyl Butene-l H? CB C OH; 3 CH3OH Isop-rene Methanol DESCRIPTION OF THE INVENTlON in order to assure optimum results. it is important Step I that the ratios of the hydroperoxide. the acid. the alco- The Oxidation of lsobumne to produce hol and the metal salt be kept within certain speci led butylhydroperoxide and t-butyl alcohol is well known in the art. as described for example in l & EC. Vol. 53. P. 655 1961 Thus. this reaction may conveniently be carried out by the liquid phase oxidation of two moles of isobutane with one and one-half moles of oxygen at a temperature of about 130 to l C and a pressure of 500 to 700 psi to produce a mixture of tbutylhydroperoxide and t-butyl alcohol. This mixture may readily be separated by distillation and each of the products recovered for use in subsequent steps. Step 2 The t-butylhydroperoxide obtained in Step 1 (or from any other known source) is then converted to methylal and t-butyl alcohol by reacting the hydroperoxide with methanol in the presence of an acid catalyst. Preferably. a selected metal salt co-catalyst is also employed to enhance both the yield and reaction rate.

This process may be carried out by mixing the t-butyl hydroperoxide in the methanolic acid medium for about one-half to 5 hours at a temperature of from about 20 to 80 C. preferably under autogenous pressure. and then recovering the resulting methylal and tbutyl alcohol mixture. which may be separated by flash distillation.

As stated above. it is preferred that a metal salt catalyst also be employed. These salts are those whose metals are from groups lB. VI. VII or VlIl or the Periodic Table. and whose anions. while not critical, are preferably the sulfate. nitrate. oxide. oxalate or chloride. Amongst the metals. cobalt. iron. copper. nickel. manganese and chromium are preferred.

The acids employed are generally concentrated mineral acids such as hydrochloric. phosphoric. polyphosphoric. sulfuric or perchloric. although sulfuric acids or acid-treated molecular sieves may also be employed. The preferred acid is sulfuric acid. which may be used in concentrations of from about 90 percent to 20 percent oleum.

ranges. Thus. the alcohol should be present in a 2-tol 2 fold molar excess. based on the moles of hydroperoxide. and preferably from about a 7-to-l0 fold molar excess of the alcohol.

The amount of acid should, as mentioned above, be based on the amount of alcohol present in order to provide about a l to 4 weight percent concentration of the acid based on the total weight of the acid-alcohol mixture. The preferred weight percent of acid is about 2 to 3 percent. Although amounts below 1 percent may be employed. it is essential that the acid concentration not exceed about 4 percent, since at higher concentrations the formation of ether is favored to the exclusion of tbutyl alcohol.

The amount of metal salt catalyst used should be in the range of from about 0.1 to 5.0 grams per 50 to grams of alcohol-acid solution. and preferably from about 1.0 to 3.0 grams.

Step 3 The t-butyl alcohol obtained in Steps 1 and/or 2 may readily be converted to isobutylene by conventional dehydration procedures such as are described in U.S.S.R. Pat. No. 127,252 (March 25. 1960); CA 1960. l9680i; or British Patent No. 576.480 (1946).

Thus. for example. by heating t-butyl alcohol in the presence of silico-tungstic acid at a temperature of from to 100 C for at least one hour at atmospheric pressure there is obtained isobutylene in yields in excess of percent.

Step 4 The isobutylene obtained in Step 3 and the methylal obtained in Step 2 are then reacted to form a mixturev containing minor amounts of isoprene and methyl tbutyl ether and a major amount of isoprene precursors; namely. a mixture of l.3-dimethoxy-3-methylbutane and 4-methoxy-2-methylbutene-l. together with small amounts of methyl t-butyl ether and isoprene.

This reaction is advantageously carried out by reacting the isobutylene with methylal in the presence of a Lewis acid or solid acid catalyst for from 1 to 7 hours, and preferably 3 to 4 hours, at a temperature of from about to 100 C, and preferably at room temperature. It is essential that this reaction be carried out under anhydrous conditions to avoid as much as possible the formation of ethers.

The acid catalysts which may be used include boron trifluoride, boron trifluoride etherate boron trifluoride in phosphoric acid, boron trifluoride on alumina, stannic chloride, aluminum bromide, sulfuric acid and titanium tetrachloride, of which boron trifluoride catalyst is preferred. The amount of catalyst used should desirably be in the range of from 5 to grams of catalyst per 100 grams of total reactants, but this ratio is not critical.

The ratio of isobutylene to methylal is not critical either and may vary from equimolar amounts to an excess of either reactant.

Neutralization of the product mixture with any suitable alkaline material. followed by separation of the catalyst phase from the product phase yields a product mixture of the aforesaid isoprene precursors comprising principally 1,3-dimethoxy-3-methylbutane admixed with small amounts of 4-methoxy-2-methylbutene-l. methyl t-butyl ether and isoprene. This mixture need not be separated since the total mixture is then treated in the next step as described below.

Step 5 The product mixture obtained from Step 4, and containing a major proportion of l.3-dimethoxy-3- methylbutane together with minor amounts of 4-methoxy-2-methylbutene-l methyl t-butyl ether and isoprene, is then pyrolyzed at temperatures of from 175 to 350 C. and preferably at about 200 C. in the presence of an acid catalyst, to form a mixture of isoprene and methanol. The methanol, after separation from the isoprene by distillation, is desirably recycled to Step 2 of this process.

The acid catalyst employed in this step include such materials as ion exchange resins, for example Amberlyst resins (polystryene-sulfuric acid type resins made by Rohm and Haas, Philadelphia, Pa); molecular sieve catalysts of the silica/alumina type (such as Linde SK- 400 mole sieve made by Linde Division of Union Carbide Corporation. N.Y.); or organic acids such as ptoluene sulfonic acid.

Together with the acid catalyst, there may be employed organic solvents such as dimethylformamide or n-methyl-Z-pyrolidone, in amounts of approximately equal weights of solvent and feedstock. When the reaction is carried out without a solvent, there may be employed instead a fixed bed catalyst reactor, over which the feed material may be passed.

EXAMPLE 1 Step 1 Reactions are carried out in a stainless steel reactor with a 1,000 psig pressure rating. The charge consists of 400 grams of isobutane with 1 gram of di-t-butyl peroxide as an initiator. The reactor is charged with isobutane and heated to 125 C. Compressed air is then metered into the reactor through a disk filter. After 15 hours at 125 C the reactor is cooled and the product worked up. The conversion is 50 percent and the yields of t-butylhydroperoxide and t-butyl alcohol is 46 and 44 percent, respectively.

EXAMPLE 2 Step 2 Ten grams (0.1 mole) of t-butyl hydroperoxide is added to 20 grams ofa 2 percent weight solution of sulfuric acid in methanol containing 0.5 grams ofa ferrous sulfate. The reaction is stirred for 4 hours at 60 C under autogenous pressure and then is worked up by a reduced pressure flash distillation. The conversion to methylal and t-butyl alcohol is 50 percent, and the yields are 95 percent and 87 percent. respectively.

EXAMPLE 3 Ten grams (0.1 mole) of t-butyl hydroperoxide are added to 50 grams of a 1 percent weight solution of'sulfuric acid in methanol containing 1.0 grams of ferrous sulfate and the reaction run in the same manner as Example 2. The conversion of methanol to methylal and t-butyl alcohol is percent, and the yields are 90 percent and 85 percent, respectively.

EXAMPLE 4 Ten grams (0.1 mole) of t-butyl hydroperoxide are added to 30 grams of a 2 percent weight solution of phosphoric acid in methanol containing 1.0 grams of copper oxide. The reaction is stirred for 4 hours at 60 C under autogenous pressure. The conversion to methylal and t-butyl alcohol is 60 percent and the yield is 85 percent.

EXAMPLE 5 Step 3 One mole of t-butyl alcohol is passed through a continuous flow reactor containing silicotungstic acid at C and 1 atmospheric pressure to yield 50 grams (.89 mole) of isobutene.

EXAMPLE 6 One mole of t-butyl alcohol is heated with 10 grams of 5 weight percent H. 50 at 200 C at a pressure of 50 atmospheres to yield 0.80 moles of isobutene.

EXAMPLE 7 EXAMPLE 8 In accordance with the procedures of Example 7, but

using 3 grams of BF and carrying out the reaction for 1 hour, there is obtained a mixture of 1,3-dimethoxy-3- methyl butane, 4-methoxy-2-methyl butene-l, isoprene and methyl t-butyl ether in amounts of 65, 15, 3 and 9 percent, respectively.

EXAMPLE 9 In accordance with the procedures of Example 7, but using 2.0 grams of BE, with 0.25 moles of methylal and 0.25 moles of isobutylene, there is obtained a mixture of l,3-dimethoxy-3-methyl butane. 4-methoxy-2- methyl butene-l. isoprene and methyl t-butyl ether in amounts of 54. 17. 2 and 20 percent. respectively.

EXAMPLE In accordance with the procedures of Example 7, but using 0.5 moles ofisobutylene with 0.25 moles of methylal, there is obtained a mixture of l,3-dimethoxy-3- methyl butane, 4-methoxy-2-methyl butenel, isoprene and methyl t-butyl ether in amounts of 50, 18, 7 and percent. respectively.

EXAMPLE 1 1 In accordance with the procedures of Example 7, but using 6 grams of BF /H PO in place of BE, etherate. there is obtained a mixture of l.3-dimethoxy-3-methyl butane, 4 -rnethoxy-2-methyl butene-l. isoprene and methyl t-butyl ether in amounts of 35. l7, 1 and percent, respectively.

EXAMPLE 12 Step 5 A mixture containing ten grams (0.075 mole) of l,3-dimethoxy-3-methyl butane. 3.0 grams (0.02 mole) of 4-methoxy-2-methyl butene-l and 0.34 gram (.005 mole) of isoprene (a combined total of 0.] moles of charge) is passed through a reactor Containing 6.0 grams of Linde SK-400 molecular sieve at 250 C over a 3 hour interval. The yield of isoprene is 90 percent and the conversion is 95 percent. After six repetitions of this experiment, there is still no observable catalyst deterioration and the yields are still in the 90 percent range.

EXAMPLE 13 In accordance with the procedures of Example 12.

but employing 13.2 grams (0.] mole) of l,3-dimethoxy-3-methylbutane. substituting p-toluene sulfonic acid for the molecular sieve, and carrying out 8 the reaction at 50 C instead of 250 C. there is obtained a 5 percent yield of isoprene.

In accordance with the foregoing procedure, but carrying out the reaction at 200 C instead of 250 C, there is obtained an 80 percent yield of isoprene.

EXAMPLE 14 In accordance with the general procedures of Example l2. 1.3-dimethoxy-3-methyl butane is heated for 5 hours at 160 C in N-methyl-Z-pyrolidone solvent containing ZnCL. The weight ratio of solvent to starting material is 1:1; and the yield of isoprene is 80 percent.

EXAMPLE 15 Thirteen grams (0.] mole) of l,3-dimethoxy-2- methyl butane is passed through a reactor containing 6.0 grams of Amberlyst l5 resin at 300 C over a 4 hour interval. The yield of isoprene is percent and the conversion is 83 percent. No catalyst deterioration is observed after 3 runs.

What is claimed is:

l. A process for the production of methylal and tbutyl alcohol which comprises reacting tbutylhydroperoxide with methanol in the presence of an acid catalyst selected from the group consisting of mineral acids and acid treated molecular sieves at a temperature of from about 20 to 80 C, wherein the methanol is present in a 2-to-l2 fold molar excess, based on the moles of hydroperoxide. and the acid catalyst is present in not more than a four weight percent concentration based on the total weight of the acidmethanol mixture.

2. The process according to claim 1 wherein the mineral acid is sulfuric acid.

3. The process according to claim 1 wherein there is also employed a co-catalyst comprising salts of metals from groups IV, VI. VII or VIII of the Periodic table, said metals being selected from the group consisting of cobalt, iron, copper, nickel. manganese, or chromium, wherein the metal salt is present in amounts of from about 0.1 to 5.0 grams per 50 to grams of acidmethanol solution. 

1. A PROCESS FOR THE PRODUCTION OF METHYLAL AND T-BUTYL ALCOHOL WHICH COMPRISES REACTING T-BUTYLHYDROPEROXIDE WITH METHANOL IN THE PRESENCE OF AN ACID CATALYST SELECTED FROM THE GROUP CONSISTING OF MINERAL ACIDS AND ACID TREATED MOLECULAR SIEVES AT A TEMPERATURE OF FROM ABOUT 20* TO 80*C, WHEREIN THE METHANOL IS PRESENT IN A 2-TO-12 FOLD MOLAR EXCESS, BASED ON THE MOLES OF HYDROPEROXIDE, AND THE ACID CATALYST IS PRESENT IS NOT MORE THAN A FOUR WEIGHT PERCENT CONCENTRATION BASED ON THE TOTAL WEIGHT OF THE ACID-METHANOL MIXTURE.
 2. The process according to claim 1 wherein the mineral acid is sulfuric acid.
 3. The process according to claim 1 wherein there is also employed a co-catalyst comprising salts of metals from groups IV, VI, VII or VIII of the Periodic table, said metals being selected from the group consisting of cobalt, iron, copper, nickel, manganese, or chromium, wherein the metal salt is present in amounts of from about 0.1 to 5.0 grams per 50 to 75 grams of acid-methanol solution. 